1. Field of the Invention
The present invention generally relates to a method and an apparatus for microscopical measurement and, more particularly, to a method and an apparatus for surface structure measurement, integrating a scatterometer and a bright-field microscope.
2. Description of the Prior Art
With the rapid development in semiconductor processing, the feature size has advanced to 65 nm, which is smaller than the optical diffraction limit. Therefore, conventional optical microscopes are insufficient to form clear images to meet the requirements for advanced semiconductor processing.
As disclosed in “Scatterfield Microscopy Using Back Focal Plane Imaging with an Engineered Illumination Field,” Proc. Of SPIE, vol. 6152. 61520J (2006) by H. J. Patrick, R. Atota, B. M. Barnes, et al. with National Institute of Standards and Technology (NIST), bright-field microscopy is used as shown in FIG. 1. The image of a mask 11 is formed on the back focal plane 14 of an objective lens 13 using a relay system 12. The incident angle is changed according to the movement of the mask 11. A charge-coupled device (CCD) camera 15 is used to record the diffracted light at different incident angles. Even though such a structure is simpler than the conventional scatterometer, precision control for the movement of the mask is required.
In U.S. Pat. No. 7,061,623 B2, an interference microscope is used as shown in FIG. 2. The sample position or the reference plane is varied to select the incident light illuminating on the sample while the rest of light does not illuminate on the sample due to destructive interference. This patent is inventive in that an interference microscope is used to select the incident light according to the incident angle and to record the reflected light corresponding to specific incident angles. However, with such an interference microscope, precise position control is still required so as to select the incident light. Moreover, the use of an interference microscope makes system modeling more complicated and surface analysis more difficult.